Two-speed switching valve of hydraulic motor

Abstract

To reduce a manufacturing cost of a two-speed switching valve of a hydraulic motor.SOLUTION: A first annular groove 81 connected to a first actuator port 51, a second annular groove 82 connected to a second actuator port 52, a third annular groove 83 connected to a first motor port 53, a fourth annular groove 84 connected to a second motor port 54, a fifth annular groove 85 connected to a first drain port 55, and a sixth annular groove 86 connected to a second drain port 56 are formed at an internal peripheral face of an accommodation hole 71 in which a spool 75 is accommodated. The first annular groove 81 is located between the third annular groove 83 and the fifth annular groove 85, the second annular groove 82 is located between the fourth annular groove 84 and the sixth annular groove 86, the third annular groove 83 and the fourth annular groove 84 are symmetrically located with a center between the first annular groove 81 and the second annular groove 82 as a center O, and the fifth annular groove 85 and the sixth annular groove 86 are symmetrically located.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a two-speed switching valve for a hydraulic motor. [Background technology]

[0002] Patent Document 1 discloses a two-speed changeover valve that switches the capacity of a hydraulic motor. The two-speed changeover valve is connected to two two-speed pistons, a hydraulic drive circuit connected to the hydraulic motor, and a tank. When no pilot pressure is applied, the two-speed changeover valve connects the second-speed pistons to the tank, and when pilot pressure is applied, it directs motor operating pressure to the second-speed pistons. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 1-116301 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] The valve body of a two-speed switching valve such as that described in Patent Document 1 is formed with an accommodation hole in which a spool is housed, and the inner surface of the accommodation hole is formed with a plurality of annular grooves connected to ports that respectively communicate with the two-speed piston, the hydraulic motor, and the tank.

[0005] Generally, multiple annular grooves are machined by inserting different tools into both ends of the receiving hole. This requires the management of two tools, which results in poor machining efficiency and increases the manufacturing cost of the two-speed switching valve.

[0006] The present invention has been made in view of the above problems, and has an object to reduce the manufacturing cost of a two-speed switching valve for a hydraulic motor. [Means for solving the problem]

[0007] The present invention is a two-speed switching valve for a hydraulic motor, comprising a valve body, an accommodation hole formed in the valve body, and a spool accommodated in the accommodation hole and moving in response to a pilot pressure to switch between supplying and discharging working fluid to a first displacement switching actuator and a second displacement switching actuator, thereby controlling the displacement of the hydraulic motor. When no pilot pressure is applied to the spool, a first drain passage and a second drain passage are connected to the first displacement switching actuator and the second displacement switching actuator, respectively, and the hydraulic motor has a large capacity, and when pilot pressure is applied to the spool, the operating pressure of the hydraulic motor is introduced to the first displacement switching actuator or the second displacement switching actuator, and the hydraulic motor has a small capacity. The inner peripheral surface of the accommodation hole is connected to a first actuator port which is connected to the first displacement switching actuator. a first annular groove connected to a first motor port communicating with one of a pair of motor passages connected to the hydraulic motor; a second annular groove connected to a second actuator port communicating with the second displacement switching actuator; a third annular groove connected to a first motor port communicating with one of a pair of motor passages connected to the hydraulic motor; a fourth annular groove connected to a second motor port communicating with the other of the pair of motor passages connected to the hydraulic motor; a fifth annular groove connected to a first drain port communicating with the first drain passage; and a sixth annular groove connected to a second drain port communicating with the second drain passage, wherein the first annular groove is located between the third annular groove and the fifth annular groove, and the second annular groove is located between the fourth annular groove and the sixth annular groove, and the third annular groove and the fourth annular groove are located symmetrically with respect to a center of the first annular groove and the second annular groove, and the fifth annular groove and the sixth annular groove are located symmetrically with respect to a center of the first annular groove and the second annular groove.

[0008] In this invention, the first, third, and fifth annular grooves and the second, fourth, and sixth annular grooves are positioned symmetrically with respect to the centers of the first and second annular grooves. Therefore, a common tool can be inserted into one opening of the valve body's receiving hole to simultaneously machine the first, third, and fifth annular grooves, and another tool can be inserted into the other opening of the valve body's receiving hole to simultaneously machine the second, fourth, and sixth annular grooves. This allows the first through sixth annular grooves to be machined efficiently.

[0009] Furthermore, the present invention is characterized in that a seventh annular groove connected to a high-pressure selection port that guides high-pressure working fluid from one of the pair of motor passages is further formed on the inner peripheral surface of the accommodation hole, the spool having a spool insertion hole formed in the other end face opposite to the one end face on which pilot pressure acts, a sub-spool inserted in the spool insertion hole, and a pressure chamber partitioned by the spool insertion hole and the sub-spool and into which working fluid from the high-pressure selection port is guided, when the spool moves against the pilot pressure by the working fluid guided from the high-pressure selection port while the hydraulic motor is operating at a small capacity, the hydraulic motor switches to a large capacity, and the seventh annular groove is located in the middle of the first annular groove and the second annular groove.

[0010] In this invention, the first, third, and fifth annular grooves and the second, fourth, and sixth annular grooves are positioned symmetrically with respect to the seventh annular groove. Therefore, the first through seventh annular grooves can be efficiently machined. Furthermore, the spool has a sub-spool that is inserted into a spool insertion hole formed in one end face and defines a pressure chamber, and thus is not a symmetrical structure. Although the spool is not a symmetrical structure, each annular groove is symmetrical, so each annular groove can be efficiently machined. [Effects of the Invention]

[0011] According to the present invention, it is possible to reduce the manufacturing cost of the two-speed switching valve for the hydraulic motor. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a hydraulic circuit diagram including a two-speed selector valve according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view of a two-speed selector valve according to an embodiment of the present invention, showing the case where the valve is in a low speed position. [Figure 3] 1 is a cross-sectional view of a two-speed selector valve according to an embodiment of the present invention, showing the case where the valve is in a high-speed position. [Figure 4]FIG. 3 is a cross-sectional view of a valve body of a two-speed switching valve, showing the arrangement of first to seventh annular grooves. [Figure 5] FIG. 10 is a cross-sectional view of a two-speed selector valve according to a modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a two-speed switching valve 100 for a hydraulic motor 1 according to an embodiment of the present invention will be described with reference to the drawings.

[0014] The hydraulic motor 1 is mounted on a work machine such as a hydraulic excavator (not shown) and functions as a drive source for the travel device of the work machine. The two-speed selector valve 100 changes the capacity of the hydraulic motor 1 to switch the operating speed of the hydraulic motor 1. Note that, although the following description will be given of a case where hydraulic oil is used as the working fluid, other liquids such as a water-soluble substitute liquid may be used instead of hydraulic oil.

[0015] First, with reference to Figure 1, a hydraulic circuit for driving the hydraulic motor 1 will be described. In this embodiment, the hydraulic motor 1 is a swash plate-type hydraulic piston motor whose displacement volume changes depending on the tilt angle of a swash plate 7. A pair of motor passages 31, 32 are connected to the hydraulic motor 1. One of the pair of motor passages 31, 32 is connected to a pump (not shown) and the other is connected to a tank T depending on the position of a control valve (not shown). When hydraulic oil is supplied from the pump to the first motor passage 31, the rotating shaft 1a rotates in the forward direction, and when hydraulic oil is supplied from the pump to the second motor passage 32, the rotating shaft 1a rotates in the reverse direction. The rotation of the rotating shaft 1a of the hydraulic motor 1 is transmitted to the drive wheels of the work machine via a reducer (not shown).

[0016] The hydraulic motor 1 has a first capacity switching actuator 21 and a second capacity switching actuator 22 that switch the capacity of the hydraulic motor 1 by switching the tilt angle of the swash plate 7, a swash plate spring 11 that urges the swash plate 7 in the direction that increases the capacity of the hydraulic motor 1, and a cylinder 26 for releasing the parking brake 25.

[0017] The tilt angle of the swash plate 7 changes depending on the biasing force of the swash plate spring 11 and the thrusts of the first and second displacement switching actuators 21 and 22.

[0018] In the parking brake 25, when hydraulic oil is not introduced to the release cylinder 26, the rotation of the hydraulic motor 1 is braked by the biasing force of the brake spring 27, and when hydraulic oil is introduced to the release cylinder 26 through the brake release passage 29, the braking force of the brake spring 27 is released.

[0019] A counterbalance valve 40 is provided in the pair of motor passages 31, 32. The counterbalance valve 40 allows the hydraulic motor 1 to operate while maintaining the hydraulic motor 1 in a stopped state. The counterbalance valve 40 has a first operating position 40A, a second operating position 40B, and a stop position 40C. When hydraulic oil is supplied from the pump to the first motor passage 31, the counterbalance valve 40 is set to the first operating position 40A by the pilot pressure in a pilot chamber 41a. When hydraulic oil is supplied from the pump to the second motor passage 32, the counterbalance valve 40 is set to the second operating position 40B by the pilot pressure in a pilot chamber 41b. When hydraulic oil is not supplied to the first motor passage 31 or the second motor passage 32, the counterbalance valve 40 is set to the stop position 40C by the biasing forces of springs 42a, 42b.

[0020] In the first operating position 40A, the counterbalance valve 40 allows hydraulic oil to flow to the hydraulic motor 1 through the first motor passage 31 via the check valve 43, and allows hydraulic oil to be discharged from the hydraulic motor 1 through the second motor passage 32. The counterbalance valve 40 also directs hydraulic oil to the release cylinder 26 through the brake release passage 29, thereby releasing the parking brake 25. In the second operating position 40B, the counterbalance valve 40 allows hydraulic oil to flow to the hydraulic motor 1 through the second motor passage 32 via the check valve 44, and allows hydraulic oil to be discharged from the hydraulic motor 1 through the first motor passage 31. The counterbalance valve 40 also directs hydraulic oil to the release cylinder 26 through the brake release passage 29, thereby releasing the parking brake 25. In the stop position 40C, the counterbalance valve 40 uses the check valves 43 and 44 to block the flow of hydraulic oil discharged from the hydraulic motor 1. Additionally, the hydraulic oil in the release cylinder 26 is discharged to the tank T through the brake release passage 29. As a result, the parking brake 25 is activated.

[0021] The two-speed switching valve 100 has a first actuator port 51 communicating with the first displacement switching actuator 21, a second actuator port 52 communicating with the second displacement switching actuator 22, a first motor port 53 communicating with the first motor passage 31, a second motor port 54 communicating with the second motor passage 32, a first drain port 55 communicating with the first drain passage 33, and a second drain port 56 communicating with the second drain passage 34.

[0022] The two-speed switching valve 100 further has a pilot chamber 63 to which pilot pressure is introduced through a pilot passage 66, and a pressure chamber 64 to which the high-pressure hydraulic oil from the pair of motor passages 31, 32 is introduced.

[0023] When an operating lever (not shown) for switching the travel speed of the work machine between low speed and high speed is operated by the operator to the high speed side, pilot pressure is introduced from the pilot pressure supply source to the pilot chamber 63, and when the operating lever is operated to the low speed side, pilot pressure is not introduced to the pilot chamber 63. Note that an operating switch may be used instead of the operating lever.

[0024] Hydraulic oil is introduced into the pressure chamber 64 through a pressure introducing passage 65 connected to the counterbalance valve 40. When the counterbalance valve 40 is in the first operating position 40A, the pressure in the first motor passage 31 is introduced into the pressure chamber 64 through the pressure introducing passage 65, and when the counterbalance valve 40 is in the second operating position 40B, the pressure in the second motor passage 32 is introduced into the pressure chamber 64 through the pressure introducing passage 65. In this way, the hydraulic oil with the higher pressure from the pair of motor passages 31, 32 is selected and introduced into the pressure chamber 64.

[0025] The two-speed switching valve 100 is a two-position type switching valve having a low-speed position 50A and a high-speed position 50B.

[0026] When the operating lever is operated to the low-speed side, pilot pressure is not introduced into the pilot chamber 63, and the pressure in the pressure chamber 64 causes the two-speed switching valve 100 to assume the low-speed position 50A (the state shown in FIG. 1). In the low-speed position 50A, the first drain port 55 and the second drain port 56 are connected to the first actuator port 51 and the second actuator port 52, respectively, and the first motor port 53 and the second motor port 54 are blocked. As a result, the hydraulic oil in the first and second displacement switching actuators 21 and 22 is discharged to the tank T, and the tilt angle of the swash plate 7 is maximized by the biasing force of the swash plate spring 11, and the hydraulic motor 1 assumes a large capacity. As a result, the hydraulic motor 1 operates at low speed.

[0027] When the control lever is operated toward the high-speed side, pilot pressure is introduced into the pilot chamber 63, causing the two-speed selector valve 100 to assume the high-speed position 50B. In the high-speed position 50B, the first motor port 53 and the second motor port 54 are connected to the first actuator port 51 and the second actuator port 52, respectively, while the first drain port 55 and the second drain port 56 are blocked. As a result, the operating pressure of the hydraulic motor 1 is introduced from the first motor passage 31 or the second motor passage 32 to the first displacement switching actuator 21 or the second displacement switching actuator 22, thereby minimizing the tilt angle of the swash plate 7 due to the thrust of the first displacement switching actuator 21 or the second displacement switching actuator 22, thereby reducing the displacement of the hydraulic motor 1. As a result, the hydraulic motor 1 operates at high speed.

[0028] Furthermore, when the operating lever is on the high-speed side and the two-speed selector valve 100 is in the high-speed position 50B, for example, when the work machine is going up a slope, the load on the hydraulic motor 1 increases, and the operating pressure of the hydraulic motor 1 increases, causing the pressure introduced from the counterbalance valve 40 to the pressure chamber 64 through the pressure introducing passage 65 to increase. When the load due to the pressure in the pressure chamber 64 exceeds the load due to the pilot pressure in the pilot chamber 63, the two-speed selector valve 100 automatically switches from the high-speed position 50B to the low-speed position 50A. This causes the hydraulic motor 1 to switch to a larger capacity, increasing torque. In this way, when the load on the hydraulic motor 1 increases, the motor capacity automatically increases and the driving force increases, improving the operability of the work machine.

[0029] Next, the structure of the two-speed switching valve 100 will be described with reference to Figures 2 and 3. Figure 2 is a cross-sectional view of the two-speed switching valve 100 when in the low-speed position 50A, and Figure 3 is a cross-sectional view of the two-speed switching valve 100 when in the high-speed position 50B. In Figures 2 and 3, components that are assigned the same reference numerals as those shown in Figure 1 have the same configuration as that shown in Figure 1.

[0030] The two-speed switching valve 100 includes a valve body 70, a housing hole 71 formed in the valve body 70, and a spool 75 housed in the housing hole 71. The spool 75 moves in response to the pilot pressure in the pilot chamber 63 to switch between supplying and discharging hydraulic oil to the first displacement switching actuator 21 and the second displacement switching actuator 22, thereby controlling the displacement of the hydraulic motor 1.

[0031] The accommodation hole 71 is a hole with openings at both ends, and the spool 75 moves along the inner circumferential surface. The openings at both ends of the accommodation hole 71 are sealed by plugs 90, 91, respectively. A pilot chamber 63 is defined between the plug 90 and one end face 75d of the spool 75, and pilot pressure acts on the one end face 75d of the spool 75. A part of the pilot passage 66 is formed in the plug 90.

[0032] The spool 75 has a spool insertion hole 76 formed in an end face 75e opposite to an end face 75d on which the pilot pressure acts, and a sub-spool 77 slidably inserted into the spool insertion hole 76. The pressure chamber 64 is defined by the spool insertion hole 76 and the sub-spool 77.

[0033] The inner circumferential surface of the accommodation hole 71 is formed with a circular opening including a first actuator port 51, a second actuator port 52, a first motor port 53, a second motor port 54, a first drain port 55, a second drain port 56, and a high-pressure selection port 57 that guides high-pressure working fluid from one of the pair of motor passages 31, 32 to the pressure chamber 64. The three ports, namely the first actuator port 51 and the first motor port 53 and the first drain port 55 that selectively communicate therewith, and the three ports, namely the second actuator port 52 and the second motor port 54 and the second drain port 56 that selectively communicate therewith, are positioned symmetrically with respect to the high-pressure selection port 57.

[0034] The inner circumferential surface of the accommodation hole 71 is further formed with a brake release port 58 that communicates with the brake release passage 29 and a third drain port 59 that communicates with the tank T, each of which has a circular opening. The brake release port 58 is formed opposite the high-pressure selection port 57. The third drain port 59 communicates with a drain chamber 78 that is defined by the other end surface 75 e of the spool 75 and the plug 91.

[0035] The inner peripheral surface of the accommodation hole 71 is formed with a first annular groove 81 connected to the first actuator port 51, a second annular groove 82 connected to the second actuator port 52, a third annular groove 83 connected to the first motor port 53, a fourth annular groove 84 connected to the second motor port 54, a fifth annular groove 85 connected to the first drain port 55, a sixth annular groove 86 connected to the second drain port 56, and a seventh annular groove 87 connected to the high-pressure selection port 57 and the brake release port 58. The first to seventh annular grooves 81 to 87 are grooves formed annularly around the entire circumference of the inner peripheral surface of the accommodation hole 71.

[0036] The outer peripheral surface of spool 75 is formed with a first spool groove 75a that connects first annular groove 81 and third annular groove 83 at high speed position 50B, a second spool groove 75b that connects first annular groove 81 and fifth annular groove 85 at low speed position 50A, and a third spool groove 75c that connects second annular groove 82 and sixth annular groove 86 at low speed position 50A and connects second annular groove 82 and fourth annular groove 84 at high speed position 50B. The first to third spool grooves 75a, 75b, and 75c are grooves formed annularly around the entire outer peripheral surface of spool 75.

[0037] A passage 79 is formed in the spool 75, which connects the pressure chamber 64 with the seventh annular groove 87 and guides hydraulic oil from the high-pressure selection port 57 to the pressure chamber 64, as well as from the pressure chamber 64 to the brake release port 58.

[0038] The operation of the two-speed selector valve 100 configured as above will now be described.

[0039] When the operating lever is operated to the low-speed side and the two-speed switching valve 100 is in the low-speed position 50A, pilot pressure is not conducted to the pilot chamber 63, but the operating pressure of the hydraulic motor 1 is conducted to the pressure chamber 64 through the high-pressure selection port 57. As a result, as shown in FIG. 2, the pressure in the pressure chamber 64 applies a load to the spool 75 and the sub-spool 77 in a direction that expands the pressure chamber 64, causing the spool 75 to contact the plug 90 and the sub-spool 77 to contact the plug 91. In this state, the first annular groove 81 and the fifth annular groove 85 communicate with each other through the second spool groove 75b, and the second annular groove 82 and the sixth annular groove 86 communicate with each other through the third spool groove 75c. Therefore, the first drain port 55 and the second drain port 56 communicate with the first actuator port 51 and the second actuator port 52, respectively, and the first motor port 53 and the second motor port 54 are blocked. This allows the hydraulic motor 1 to have a large capacity and operate at a low speed, as described above.

[0040] When the operating lever is operated to the high-speed side and the two-speed selector valve 100 is in the high-speed position 50B, pilot pressure is introduced to the pilot chamber 63, while the operating pressure of the hydraulic motor 1 is introduced to the pressure chamber 64 through the high-pressure selection port 57. As a result, as shown in FIG. 3 , the load calculated from the pilot pressure in the pilot chamber 63 and the pressure-receiving area of ​​the spool 75 becomes greater than the load calculated from the pressure in the pressure chamber 64 and the pressure-receiving area of ​​the sub-spool 77, and the spool 75 receives a load in a direction that expands the pilot chamber 63, causing it to come into contact with the plug 91. At this time, the drain chamber 78 defined between the spool 75 and the plug 91 is connected to the tank T through the third drain port 59, so the spool 75 moves smoothly. The sub-spool 77 remains in contact with the plug 91. In this state, the first annular groove 81 and the third annular groove 83 communicate with each other via the first spool groove 75a, and the second annular groove 82 and the fourth annular groove 84 communicate with each other via the third spool groove 75c, so that the first motor port 53 and the second motor port 54 communicate with the first actuator port 51 and the second actuator port 52, respectively, and the first drain port 55 and the second drain port 56 are blocked. As a result, as described above, the hydraulic motor 1 has a small capacity and operates at high speed.

[0041] Furthermore, when the operation lever is on the high-speed side and the two-speed switching valve 100 is in the high-speed position 50B, if the load on the hydraulic motor 1 increases, the load calculated from the pressure in the pressure chamber 64 and the pressure-receiving area of ​​the sub-spool 77 becomes larger than the load calculated from the pilot pressure in the pilot chamber 63 and the pressure-receiving area of ​​the spool 75, and the spool 75 moves against the pilot pressure in the pilot chamber 63 and comes into contact with the plug 90 (the state shown in FIG. 1). The sub-spool 77 maintains contact with the plug 91. In this way, if the spool 75 moves against the pilot pressure due to hydraulic oil guided from the high-pressure selection port 57 while the hydraulic motor 1 is operating at a small capacity, the two-speed switching valve 100 automatically switches from the high-speed position 50B to the low-speed position 50A, and the hydraulic motor 1 switches to a large capacity.

[0042] Next, the arrangement and processing method of the first to seventh annular grooves 81-87 formed on the inner circumferential surface of the accommodation hole 71 will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view of the valve body 70 of the two-speed switching valve 100, showing the arrangement of the first to seventh annular grooves 81-87.

[0043] The first annular groove 81 is located between the third annular groove 83 and the fifth annular groove 85, and the second annular groove 82 is located between the fourth annular groove 84 and the sixth annular groove 86. With the center of the first annular groove 81 and the second annular groove 82 as the center O, the third annular groove 83 and the fourth annular groove 84 are located symmetrically, and the fifth annular groove 85 and the sixth annular groove 86 are located symmetrically.

[0044] The seventh annular groove 87 is located in the center between the first annular groove 81 and the second annular groove 82. In other words, the first, third, and fifth annular grooves 81, 83, and 85 and the second, fourth, and sixth annular grooves 82, 84, and 86 are located symmetrically with respect to the seventh annular groove 87.

[0045] Specifically, the center O of the first annular groove 81 and the second annular groove 82 coincides with the center of the seventh annular groove 87. The dimensions from the center O to both widthwise ends of the seventh annular groove 87 are L1 and are the same. The dimensions from the center O to one widthwise end of the fifth annular groove 85 and one widthwise end of the sixth annular groove 86 are L2 and are the same. The dimensions from the center O to the other widthwise end of the fifth annular groove 85 and the other widthwise end of the sixth annular groove 86 are L3 and are the same. The dimensions from the center O to one widthwise end of the first annular groove 81 and one widthwise end of the second annular groove 82 are L4 and are the same. The dimensions from the center O to the other widthwise end of the first annular groove 81 and the other widthwise end of the second annular groove 82 are L5 and are the same. The dimensions from the center O to one widthwise end of the third annular groove 83 and one widthwise end of the fourth annular groove 84 are L6 and are the same. The dimension from the center O to the other end of the third annular groove 83 in the width direction and the dimension from the center O to the other end of the fourth annular groove 84 in the width direction are the same, L7. In this embodiment, the first to sixth annular grooves 81 to 86 have the same width dimension, and the width dimension of the seventh annular groove 87 is different from the width dimensions of the first to sixth annular grooves 81 to 86. In this embodiment, the width dimension of the seventh annular groove 87 is larger than the width dimensions of the first to sixth annular grooves 81 to 86, but it may be the same as or smaller than the width dimensions of the first to sixth annular grooves 81 to 86.

[0046] The first to seventh annular grooves 81-87 are machined on the inner circumferential surface of the receiving hole 71 using a tool (not shown) in two separate processes separated by the center O. In the first process, a tool having teeth corresponding to the third annular groove 83, the first annular groove 81, the fifth annular groove 85, and the seventh annular groove 87 is inserted through one opening 71a of the receiving hole 71 of the rotating valve body 70, and the third annular groove 83, the first annular groove 81, the fifth annular groove 85, and the seventh annular groove 87 are simultaneously machined at predetermined positions on the inner circumferential surface of the receiving hole 71. Because the third annular groove 83, the first annular groove 81, and the fifth annular groove 85 all have the same width, the third annular groove 83, the first annular groove 81, and the fifth annular groove 85 can be simultaneously machined by feeding the tool in the axial direction of the receiving hole 71 during cutting. As for the seventh annular groove 87, a portion of the groove is machined from one end in the width direction (the left end in FIG. 4 ) to a position beyond the center O.

[0047] Next, in the second step, the same tool as used in the first step is inserted through one opening 71b of the accommodation hole 71 of the rotating valve body 70, and a fourth annular groove 84, a second annular groove 82, a sixth annular groove 86, and a seventh annular groove 87 are simultaneously cut at predetermined positions on the inner circumferential surface of the accommodation hole 71. Because the fourth annular groove 84, the second annular groove 82, and the sixth annular groove 86 have the same width, the fourth annular groove 84, the second annular groove 82, and the sixth annular groove 86 can be simultaneously cut by feeding the tool in the axial direction of the accommodation hole 71. As for the seventh annular groove 87, a portion from the other end in the width direction (the right end in FIG. 4 ) to a position beyond the center O is machined. Only the seventh annular groove 87 is machined in two steps, the first step and the second step.

[0048] As described above, the first, third, and fifth annular grooves 81, 83, and 85 and the second, fourth, and sixth annular grooves 82, 84, and 86 are positioned symmetrically with respect to the seventh annular groove 87, allowing for the use of a common tool. If the first, third, and fifth annular grooves 81, 83, and 85 and the second, fourth, and sixth annular grooves 82, 84, and 86 were not symmetrical with respect to the seventh annular groove 87, two tools would be required: one inserted through the opening 71a of the accommodation hole 71 and the other inserted through the opening 71b of the accommodation hole 71. This would require the maintenance of two tools, increasing manufacturing costs. However, in this embodiment, the tools can be consolidated into one, allowing for a reduction in manufacturing costs of the two-speed switching valve 100.

[0049] Furthermore, when processing is performed without feeding the tool in the axial direction of the accommodating hole 71, for example, when pressing the mold (tool) against the inner surface of the accommodating hole 71, even if the widths of the first to sixth annular grooves 81 to 86 are not the same, the third annular groove 83, the first annular groove 81, and the fifth annular groove 85 can be processed simultaneously, and the fourth annular groove 84, the second annular groove 82, and the sixth annular groove 86 can be processed simultaneously.

[0050] Furthermore, the first to seventh annular grooves 81 to 87 may be formed by rotating a tool and feeding it in the axial direction of the receiving hole 71 while the valve body 70 is fixed.

[0051] According to the above embodiment, the following effects are achieved.

[0052] The first, third, and fifth annular grooves 81, 83, and 85 and the second, fourth, and sixth annular grooves 82, 84, and 86 are positioned symmetrically with respect to the seventh annular groove 87. Therefore, a common tool can be inserted from one opening 71a of the accommodation hole 71 to simultaneously machine the third annular groove 83, the first annular groove 81, the fifth annular groove 85, and the seventh annular groove 87, and another tool can be inserted from the other opening 71b of the accommodation hole 71 to simultaneously machine the fourth annular groove 84, the second annular groove 82, the sixth annular groove 86, and the seventh annular groove 87. Therefore, the first to seventh annular grooves 81 to 87 can be efficiently machined, thereby reducing the manufacturing cost of the two-speed changeover valve 100.

[0053] Furthermore, the spool 75 of the two-speed switching valve 100 does not have a symmetrical structure, but has a sub-spool 77 that is inserted into a spool insertion hole 76 formed in one end face 75e and defines the pressure chamber 64. Despite the spool 75 not having a symmetrical structure, the first, third, and fifth annular grooves 81, 83, and 85 and the second, fourth, and sixth annular grooves 82, 84, and 86 formed in the accommodation hole 71 of the valve body 70 are positioned symmetrically with respect to the seventh annular groove 87. Thus, although the spool 75 of the two-speed switching valve 100 does not have a symmetrical structure, each annular groove is symmetrical, and therefore each annular groove can be machined efficiently.

[0054] Next, a modification of this embodiment will be described.

[0055] (1) FIG. 5 shows a two-speed selector valve 200 according to a modification of the above embodiment. FIG. 5 is a cross-sectional view of the two-speed selector valve 200. In FIG. 5, components having the same functions as those in the above embodiment are denoted by the same reference numerals. The two-speed selector valve 200 does not have the function of automatically switching from the high-speed position 50B to the low-speed position 50A, and does not have a parking brake 25. Therefore, the valve body 70 does not have a high-pressure selection port 57 or a brake release port 58, and the inner circumferential surface of the accommodation hole 71 does not have a seventh annular groove 87. The two-speed selector valve 200 has a spring 95 as a biasing member that biases the spool 75 from the side opposite the pilot chamber 63. When no pilot pressure is applied to the pilot chamber 63, the spool 75 is biased by the spring 95 to the low-speed position 50A (the state of the upper half of the spool 75 in FIG. 5), and when pilot pressure is applied to the pilot chamber 63, the spool 75 moves against the biasing force of the spring 95 to the high-speed position 50B (the state of the lower half of the spool 75 in FIG. 5). In the two-speed switching valve 200, similar to the two-speed switching valve 100 according to the above embodiment, the third annular groove 83 and the fourth annular groove 84 are positioned symmetrically with respect to the center O of the first annular groove 81 and the second annular groove 82, and the fifth annular groove 85 and the sixth annular groove 86 are positioned symmetrically.

[0056] (2) In the two-speed switching valves 100, 200, the third annular groove 83 connected to the first motor port 53 is located closer to the opening 71a of the accommodating hole 71 than the first annular groove 81 connected to the first actuator port 51, while the fifth annular groove 85 connected to the first drain port 55 is located closer to the center of the accommodating hole 71. Similarly, the fourth annular groove 84 connected to the second motor port 54 is located closer to the opening 71b of the accommodating hole 71 than the second annular groove 82 connected to the second actuator port 52, while the sixth annular groove 86 connected to the second drain port 56 is located closer to the center of the accommodating hole 71. Alternatively, the positions of the third annular groove 83 and the fifth annular groove 85 may be opposite with respect to the first annular groove 81, and the positions of the fourth annular groove 84 and the sixth annular groove 86 may be opposite with respect to the second annular groove 82. In this case, it is necessary to change the first to third spool grooves 75a, 75b, 75c formed on the outer peripheral surface of the spool 75. In this way, the first annular groove 81 may be located between the third annular groove 83 and the fifth annular groove 85, and the second annular groove 82 may be located between the fourth annular groove 84 and the sixth annular groove 86.

[0057] (3) In the two-speed switching valve 100 according to the above embodiment, a spring may be provided as a biasing member that biases the spool 75 from the side opposite the pilot chamber 63. Specifically, the spring may be compressed and disposed between the end face 75e of the spool 75 and the plug 91.

[0058] The configuration, operation, and effects of the embodiment of the present invention will be described below.

[0059] The two-speed switching valves 100, 200 for the hydraulic motor 1 include a valve body 70, an accommodation hole 71 formed in the valve body 70, and a spool 75 accommodated in the accommodation hole 71 and moving in response to a pilot pressure to switch between supplying and discharging working fluid to the first displacement switching actuator 21 and the second displacement switching actuator 22, thereby controlling the capacity of the hydraulic motor 1. When no pilot pressure is applied to the spool 75, the first drain passage 33 and the second drain passage 34 are connected to the first displacement switching actuator 21 and the second displacement switching actuator 22, respectively, and the hydraulic motor 1 has a large capacity. When the pilot pressure is applied to the spool 75, the operating pressure of the hydraulic motor 1 is introduced to the first displacement switching actuator 21 or the second displacement switching actuator 22, and the hydraulic motor 1 has a small capacity. The inner circumferential surface of the accommodation hole 71 is provided with a first actuator port 51 connected to the first displacement switching actuator 21. a first annular groove 81, a second annular groove 82 connected to a second actuator port 52 communicating with the second displacement switching actuator 22, a third annular groove 83 connected to a first motor port 53 communicating with one of a pair of motor passages 31, 32 connected to the hydraulic motor 1, a fourth annular groove 84 connected to a second motor port 54 communicating with the other of the pair of motor passages 31, 32 connected to the hydraulic motor 1, and a first drain port 55 communicating with the first drain passage 33. 5, and a sixth annular groove 86 connected to the second drain port 56 which is in communication with the second drain passage 34. The first annular groove 81 is located between the third annular groove 83 and the fifth annular groove 85, and the second annular groove 82 is located between the fourth annular groove 84 and the sixth annular groove 86. With the center of the first annular groove 81 and the second annular groove 82 as the center O, the third annular groove 83 and the fourth annular groove 84 are located symmetrically, and the fifth annular groove 85 and the sixth annular groove 86 are located symmetrically.

[0060] In this configuration, the first, third, and fifth annular grooves 81, 83, and 85 and the second, fourth, and sixth annular grooves 82, 84, and 86 are positioned symmetrically with respect to the center O of the first annular groove 81 and the second annular groove 82. Therefore, a common tool can be inserted from one opening 71a of the accommodation hole 71 of the valve body 70 to simultaneously machine the first, third, and fifth annular grooves 81, 83, and 85, and another tool can be inserted from the other opening 71b of the accommodation hole 71 of the valve body 70 to simultaneously machine the second, fourth, and sixth annular grooves 82, 84, and 86. Therefore, the first to sixth annular grooves 81 to 86 can be efficiently machined, thereby reducing the manufacturing cost of the two-speed switching valves 100, 200 for the hydraulic motor 1.

[0061] In addition, a seventh annular groove 87 is further formed on the inner surface of the accommodating hole 71, which is connected to the high-pressure selection port 57 that guides the high-pressure working fluid from the pair of motor passages 31, 32.When the hydraulic motor 1 is operating at a small capacity, if the spool 75 moves against the pilot pressure due to the working fluid guided from the high-pressure selection port 57, the hydraulic motor 1 switches to a large capacity, and the seventh annular groove 87 is located in the center of the first annular groove 81 and the second annular groove 82.

[0062] In this configuration, the first, third, and fifth annular grooves 81, 83, and 85 and the second, fourth, and sixth annular grooves 82, 84, and 86 are positioned symmetrically with respect to the seventh annular groove 87. Therefore, the first to seventh annular grooves 81 to 87 can be machined efficiently.

[0063] The spool 75 also has a spool insertion hole 76 formed in the other end face 75e opposite to the one end face 75d on which the pilot pressure acts, a sub-spool 77 inserted into the spool insertion hole 76, and a pressure chamber 64 partitioned by the spool insertion hole 76 and the sub-spool 77 and into which the working fluid from the high-pressure selection port 57 is guided.

[0064] In this configuration, spool 75 is not symmetrical, and has a sub-spool 77 that is inserted into a spool insertion hole 76 formed in one end face 75d and defines pressure chamber 64. Although spool 75 is not symmetrical, each of annular grooves 81-87 is symmetrical, and therefore each of annular grooves 81-87 can be machined efficiently.

[0065] Although an embodiment of the present invention has been described above, the above embodiment merely shows one application example of the present invention, and is not intended to limit the technical scope of the present invention to the specific configuration of the above embodiment. [Explanation of symbols]

[0066] 100,200... Two-speed switching valve, 1... Hydraulic motor, 21... First displacement switching actuator, 22... Second displacement switching actuator, 31... First motor passage, 32... Second motor passage, 33... First drain passage, 34... Second drain passage, 50A... Low speed position, 50B... High speed position, 51... First actuator port, 52... Second actuator port, 53... First motor port, 54... Second Motor port, 55...First drain port, 56...Second drain port, 57...High pressure selection port, 63...Pilot chamber, 64...Pressure chamber, 70...Valve body, 71...Accommodating hole, 75...Spool, 76...Spool insertion hole, 77...Sub-spool, 81...First annular groove, 82...Second annular groove, 83...Third annular groove, 84...Fourth annular groove, 85...Fifth annular groove, 86...Sixth annular groove, 87...Seventh annular groove

Claims

1. A two-speed changeover valve that operates a hydraulic motor at a large capacity first speed and a small capacity second speed, A valve body and A receiving hole formed in the valve body; a spool that is accommodated in the accommodation hole and moves in response to a pilot pressure to switch between supply and discharge of working fluid to the first displacement switching actuator and the second displacement switching actuator to control the displacement of the hydraulic motor, When pilot pressure is not applied to the spool, a first drain passage and a second drain passage are connected to the first displacement switching actuator and the second displacement switching actuator, respectively, so that the hydraulic motor has a large capacity, and when pilot pressure is applied to the spool, the operating pressure of the hydraulic motor is introduced to the first displacement switching actuator or the second displacement switching actuator, so that the hydraulic motor has a small capacity, an inner circumferential surface of the accommodating hole is formed with a first annular groove connected to a first actuator port communicating with the first displacement switching actuator, a second annular groove connected to a second actuator port communicating with the second displacement switching actuator, a third annular groove connected to a first motor port communicating with one of a pair of motor passages connected to the hydraulic motor, a fourth annular groove connected to a second motor port communicating with the other of the pair of motor passages connected to the hydraulic motor, a fifth annular groove connected to a first drain port communicating with the first drain passage, a sixth annular groove connected to a second drain port communicating with the second drain passage, and a seventh annular groove connected to a high pressure selection port of the pair of motor passages for directing a high pressure working fluid therethrough, the first annular groove is located between the third annular groove and the fifth annular groove, the second annular groove is located between the fourth annular groove and the sixth annular groove, the third annular groove and the fourth annular groove are positioned symmetrically with respect to a center of the first annular groove and the second annular groove, and the fifth annular groove and the sixth annular groove are positioned symmetrically with respect to a center of the first annular groove and the second annular groove, the seventh annular groove is located at the center between the first annular groove and the second annular groove, The spool is a spool insertion hole formed in an end surface opposite to the end surface to which the pilot pressure acts; a sub-spool inserted into the spool insertion hole; a pressure chamber defined by the spool insertion hole and the sub-spool, into which the working fluid from the high pressure selection port is guided, When the hydraulic motor is operating at a low capacity, if the hydraulic fluid conducted from the high pressure selection port moves the spool against the pilot pressure, the hydraulic motor switches to a high capacity. A two-speed changeover valve for a hydraulic motor.

2. A method for manufacturing a valve body in a two-speed switching valve for operating a hydraulic motor at a large capacity first speed and a small capacity second speed, comprising the steps of: The two-speed switching valve is The valve body; A receiving hole formed in the valve body; a spool that is accommodated in the accommodation hole and moves in response to a pilot pressure to switch between supply and discharge of working fluid to the first displacement switching actuator and the second displacement switching actuator to control the displacement of the hydraulic motor, When pilot pressure is not applied to the spool, a first drain passage and a second drain passage are connected to the first displacement switching actuator and the second displacement switching actuator, respectively, so that the hydraulic motor has a large capacity, and when pilot pressure is applied to the spool, the operating pressure of the hydraulic motor is introduced to the first displacement switching actuator or the second displacement switching actuator, so that the hydraulic motor has a small capacity, an inner circumferential surface of the accommodation hole is formed with a first annular groove connected to a first actuator port communicating with the first displacement switching actuator, a second annular groove connected to a second actuator port communicating with the second displacement switching actuator, a third annular groove connected to a first motor port communicating with one of a pair of motor passages connected to the hydraulic motor, a fourth annular groove connected to a second motor port communicating with the other of the pair of motor passages connected to the hydraulic motor, a fifth annular groove connected to a first drain port communicating with the first drain passage, and a sixth annular groove connected to a second drain port communicating with the second drain passage, the first annular groove is located between the third annular groove and the fifth annular groove, the second annular groove is located between the fourth annular groove and the sixth annular groove, the third annular groove and the fourth annular groove are positioned symmetrically with respect to a center of the first annular groove and the second annular groove, and the fifth annular groove and the sixth annular groove are positioned symmetrically with respect to a center of the first annular groove and the second annular groove, The manufacturing method includes: a first process of inserting a tool having teeth corresponding to the first annular groove, the third annular groove, and the fifth annular groove from one opening of the accommodation hole of the valve body, and simultaneously cutting the first annular groove, the third annular groove, and the fifth annular groove into an inner circumferential surface of the accommodation hole; a second step of inserting the same tool as the tool from another opening of the accommodation hole of the valve body, and simultaneously cutting the second annular groove, the fourth annular groove, and the sixth annular groove into the inner circumferential surface of the accommodation hole, The tool used in the first step and the tool used in the second step are the same. A method for manufacturing a valve body comprising the steps of:

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